1. Field of the Invention
The present invention can be utilized for trunk transmission systems in which communication involves setting up paths semi-permanently on physical transmission lines, and it is suited for use in synchronous digital hierarchy (SDH) networks. A path is defined as a single and direct connection between a node-pair, for example, concatenated Virtual Container (VC) in SDH format, and may include Virtual Paths (VPs) having the same source-destination nodes in the trunk network.
2. Description of Related Art
In recent years, ultrahigh-speed trunk transmission networks that utilize the broadband nature of optical fiber have been introduced. In particular, as disclosed, a 10 Gbit/s transmission system has been introduced in trunk network links, as disclosed in:
Ref.1: Y. Kobayashi, Y. Sato, K. Aida, K. Hagimoto and K. Nakagawa, "SDH-Based 10 Gbit/s Optical Transmission System", Proc. IEEE GLOBECOM 94 (San Francisco, Calif.), pp.1166-1170, 1994 PA1 Ref.2: S. Matsuoka, N. Kawase, Y. Yamabayashi and Y. Kobayashi, "Classified Path Restoration Scheme With Hitless Protection Switching for Large-Capacity Trunk Transmission Networks", IEEE GLOBECOM 95, p.941-945, 1995 PA1 Ref.3: T.-H. Wu, "Fibre Network Service Survivability", Artech House, Boston and London, 1992 PA1 Ref.4: I. Cidon, I. Gopal, M. Kaplan and S. Kutten, "A Distributed Control Architecture of High-Speed Networks", IEEE Transactions on Communications, Vol.43, No.5, pp.1950-1960, 1995 PA1 Ref.5: A. E. Baratz, J. P. Gray, P. E. Green, Jr., J. M. Jaffe and D. P. Pozefsky, "SNA Networks of Small Systems", IEEE Journal on Selected Areas in Communications, Vol.SAC-3, No.3, pp.416-426, 1985 PA1 Ref.6: E. Oki and N. Yamanaka, "An Optimum Logical-Design Scheme for Flexible Multi-QoS ATM Networks Guaranteeing Reliability", IEICE Trans. Commun., E78-B, No.7, pp.1016-1024, 1995 PA1 Ref.7: N. Kawase, et al., "Hitless Frame Switching Scheme for SDH Networks", Trans. IEICE B-I (in Japanese), Vol.J78-B-I, No.12, pp.764-772, 1995
Meanwhile, asynchronous transfer mode (ATM), which supports diverse services, has been recommended by the ITU-T and the ATM Forum as the signal processing scheme for network nodes. In the ATM layer, which is positioned between the physical layer and the application layer, signals are processed in cell units. However, problems are encountered if the processing of signals carried in trunk network links at speeds in excess of 10 Gbit/s is carried out entirely in cell units. As many as several thousand virtual paths (VPs) have to be processed at each node, which means that large-scale node circuitry and more complex network management is required, as disclosed in:
Given this situation, the present inventors have that although the signal processing employed in the ATM layer can be utilized for service nodes, trunk network node processing functions such as path setup and restoration will be carried out in large-capacity direct-connected path units at the physical layer. These large-capacity direct-connected paths can have a variety of capacities, and the management of path networks can be simplified by processing in large-capacity direct-connected path units. It is also considered that time division multiplexing (TDM) will be used at the physical layer for multiplexing. In the present specification, it will generally be assumed that Synchronous Digital Hierarchy (SDH) is being used.
Meanwhile, high reliability and survivability are required in networks with ultrahigh-capacity links, as disclosed in:
In an ultrahigh-speed network, a failure in one fiber can have adverse effects on several thousands of users.
Self-healing functions are therefore being studied and introduced. Self-healing is a high-speed restoration function for network failures, and the best-known example to have been introduced is the SONET (Synchronous Optical Network) ring network in which path or line switches are provided. A self-healing ring network has the advantages of simpler equipment configuration and higher reliability. Problems of delay and the like mean that a multiple-ring configuration combining a plurality of rings is a promising approach to the design of trunk networks. However, a multiple-ring network with a self-healing function has not yet been achieved, and path setup functions such as routing and slot allocation have not yet been perfected.
Network supervision and control will now be explained. The TMN (Telecommunication Management Network) model has been standardized, and its architecture is shown in FIG. 1. In this architecture, a network element NE provided at each node is connected to a packet transfer network DCN (data communication network) via a message converter module MCM (or a mediation device MD, not shown), and an operating system OpS is connected to this packet transfer network DCN. FIG. 1 also shows a workstation WS for using operating system OpS. Each network element NE has a control section which exchanges control signals with the operating system OpS, and transfers supervisory and control information to the OpS, via the message converter module MCM (or a mediation device MD) and the packet network DCN.
However, as transmission link-capacity of the networks becomes larger, the cost of the operating system OpS in the model shown in FIG. 1, and in particular software development cost, becomes higher than that of the network elements NE, thus raising overall network costs. Moreover, with a centralized control network of the sort shown in the FIG. 1, if the system goes down at the control node, this leads to the entire network going down.
Distributed control has therefore been much studied. In distributed control, network control is performed in distributed fashion at each network node. FIG. 2 shows a distributed management network architecture in a single-ring network. With this architecture, a small-scale operating system OpS is provided at each network element NE. Distributed control of this sort is disclosed in, for example:
A distributed control network requires only a small-scale operating system provided in each network element, and gives higher reliability in relation to node failure than a centralized control network with several control nodes, as disclosed in:
Further advantages are that a separate control network such as DCN is not needed, the network database memory held by each node can be reduced in size, and faster control is possible.
It is anticipated that in the future there will be many different kinds of multimedia services and that each kind will require different signal quality or reliability. Trunk networks will therefore have to operate and administrate multiplexed paths for each service in accordance with a diverse range of quality requirements, and do so at low cost.
However, conventional network technology handles the quality and reliability of all paths in the same manner. Consequently, the quality and reliability of a network has previously been dictated by the path which has the highest requirements, with the result that overall network cost has been high. An approach which was studied as a way of overcoming this problem, namely, to provide for different QoS (Quality of Service) classes by means of a logically configured virtual channel handler (VCH) interconnection network layer rather than at the VP layer, is described in:
However, this proposed scheme still required a high-quality VP network and lacked flexibility at the path operating level.
It is considered that future multimedia networks will require flexibility at the path level as well. In other words, such networks will simultaneously contain paths where high cost is acceptable but loss of even a single bit is not acceptable, and other paths where some deterioration of quality or reliability is acceptable but cost should be kept low.
It is an object of the present invention to provide a solution to this problem and to achieve flexibility of path operation. It is a further object of the present invention to provide a concrete implementation, in a multiple-ring architecture under a distributed control environment, of the operation of paths that have been classified in accordance with their self-healing survivability.